DEH systems are used to control the operation of turbine-generators during each stage of operation of the turbine-generator. Commonly assigned U.S. Pat. No. 4,687, 946 to Jones describes DEH systems and turbine-generator systems and also cross references other commonly assigned patents. The '946 patent and the cross referenced patents listed in the '946 patent are hereby incorporated by reference for their teaching on DEH systems and turbine-generator systems. As used herein, turbine-generator refers to the combination of a turbine which generates rotary mechanical energy from the force of fluid or steam and a generator which converts the rotary mechanical energy generated by the turbine into electrical energy.
In turbine-generator systems, cooling water is provided to the turbine-generator and auxiliary components by cooling water regulators. Under load, the cooling water is used to help prevent the turbine-generators and auxiliary components from being damaged due to overheating. It has been found that the cooler regulators may be turned off-line during service of a turbine-generator or an auxiliary component or during a turning gear operation of the turbine-generator and not turned on-line thereafter. This situation may lead to damage to the turbine-generator or auxiliary components or may require the turbine-generator to be shutdown. In present DEH systems under ATC mode of control, the temperature of the cooling water is monitored and used to generate a hold if the temperature exceeds a certain threshold. The hold will prevent a turbine-generator from accelerating or increasing its load if the turbine-generator is in a speed or load changing mode. If a cooling regulator is off-line, however, the temperature of the cooling water may not reach an unacceptable level until the turbine-generator is fully accelerated or a load change performed. This scenario may cause shutdowns, restarts, or damage to the turbine-generator or auxiliary components.
In addition, in some DEH systems, if the system is in an OA mode of control, no holds are generated so that an unacceptable high temperature (i.e. exceeds threshold) may not prevent an operator from accelerating the turbine-generator or increasing or maintaining the current load on the turbine-generator.